Footwear has always consisted of a sole, usually stiff, which is suspended by the upper part of the foot to a position beneath the foot. The upper part of the footwear that suspends the sole has been straps, leather uppers sometimes with elastic, sometimes with shoelaces, sometimes with leather thongs, Velcro fasteners and the like which have served to attach the footwear to the foot. That type of attachment is at best sometimes comfortable. That type of attachment, even though comfortable, has common shortcomings:
(1) They must be skin-tight in order to hold the shoe on the foot.
(2) They elevate the foot onto a stiff platform.
(3) Most place the heel of the foot and the ball of the foot on different planes.
(4) All conventional footwear hangs on the foot.
The consequence of the foregoing artificial manner in which the foot is supported for contact with the ground is that the conventional footwear tends to promote atrophy of the foot muscles; muscle groupings; improper contact of the foot to the ground; constant tension in the legs, hips, back, neck, and shoulders; development of callouses, bunions and corns; reduction of the circulation in the feet and lower limbs; susceptibility of loss of balance, breaking the bones.
Cushioning in a shoe helps, but that comes at a cost: loss of stability. The most stable arrangement is a bare foot running on flat ground. When anything is put between the two, the chance for wobbling and tipping over increases. Cushioning exaggerates pronation, that is, the rotation of the foot toward the instep. Too much rocking and twisting around ankle and knee joints invariably tears or inflames muscles, tendons and ligaments. This trade off--cushioning versus stability--is the designer's dilemma, the yin and yang of athletic shoe making.